This invention relates to a communication system, and in particular to an orthogonal frequency division multiple access (OFDMA) communication system, in which each user has a frequency hopping scheme.
In an OFDMA system, the available frequency bandwidth is divided into a number of sub-channels, and these sub-channels can be allocated to different users of the system.
The document 3GPP 25.814 “Physical Layer Aspects for Evolved UTRA” v1.2.0 section 9.2.1, describes an uplink access scheme, in which each user can be allocated a variable bandwidth, formed from a number of contiguous sub-channels.
It is known that allowing frequency hopping is a way to improve the reliability of a communication system. That is, when a user is transmitting on one frequency at any given time, there is defined a sequence of frequency channels, and the user transmits on the channels of the defined sequence in turn.
However, this type of technique cannot be straightforwardly applied to a system in which variable bandwidths, and hence variable numbers of sub-channels, can be allocated to the different users, as it is a requirement that the same sub-channel should not be allocated to two different users at the same time. Moreover, it is also advantageous for the sub-channels allocated to each user to be consecutive.
Document 3GPP TSG-RAN WG1 #47BIS, Vol:R1-070203, Nr:47bis “Multiple Continuous RB Allocation Frequency Hopping in E-UTRAN Uplink” discloses a frequency hopping sequence based on Latin Square.
Document WO2006102744 discloses allocating sub-band channels wherein the sub-band channels may be divided into a tree structure.